Various attempts have been made to form nonwoven webs from biodegradable polymers. Although fibers prepared from biodegradable polymers are known, problems have been encountered with their use. For example, polylactic acid (“PLA”) is one of the most common biodegradable and sustainable (renewable) polymers used to form nonwoven webs. Unfortunately, PLA nonwoven webs generally possess a low bond flexibility and high roughness due to the high glass transition temperature and slow crystallization rate of polylactic acid. In turn, thermally bonded PLA nonwoven webs often exhibit low elongations that are not acceptable in certain applications, such as in an absorbent article. Likewise, though polylactic acid may withstand high draw ratios, it requires high levels of draw energy to achieve the crystallization needed to overcome heat shrinkage. In response to these difficulties, plasticizers have been employed in an attempt to reduce the glass transition temperature and improve bonding and softness. One common plasticizer is polyethylene glycol. Unfortunately, polyethylene glycol tends to phase separate from polylactic acid during aging, especially in high humidity and elevated temperature environment, which deteriorates the mechanical properties of the resulting fibers over time. The addition of plasticizers also causes other problems, such as degradation in melt spinning, and a reduction in melt strength and drawability.
As such, a need currently exists for polylactic fibers that exhibit good elongation properties, yet remain strong.